Besides, such ceiling grinding machines, which are suitable for grinding not only a ceiling but also for grinding walls or other surfaces, are known in the most diverse embodiments from the prior art, for example from EP 0727281 B1. Such (ceiling) grinding machines, as is also the case, for example, of the grinding machine according to EP 0727281 B1, are frequently provided in the region of the grinding-head housing with a port for an air duct leading to a vacuum cleaner, in order to extract the air contaminated with grinding dust during the grinding operation out of the grinding-head housing.
Furthermore, from DE 202005011659 U1 there is known another grinding machine of the aforesaid type, in which, in addition to the aforesaid features, there are also provided means for generating a reduced pressure inside the grinding-head housing, so that the head part of the grinding machine, or the grinding machine—because of a force resulting from the reduced pressure—is pulled toward or held against the surface to be ground.
In this connection the hood surrounding the grinding plate therein is adjustable counter to a spring force and is equipped on its rim (pointing toward the surface to be ground) with an exchangeable slip ring, which is flush with the front side of the grinding plate during the grinding operation and thereby largely or completely seals the gap between the hood and the machined surface for a suction air flow. Hereby a reduced pressure can be generated inside the hood by means of a vacuum cleaner attached to the hood, so that the head part of the grinding machine is sucked to some degree against the wall or the ceiling and if necessary is held there against the force of its total weight. By virtue of the said means for generating reduced pressure, working with such a grinding machine is made much easier and less fatiguing for the operator, since hereby he no longer has to hold any of the weight or the total weight of the grinding machine above his head, especially during ceiling-grinding work.
Nevertheless, this machine also suffers from certain disadvantages.
In the first place, a grinding machine of such design, especially if the total weight of the grinding machine is to be held in this way against a ceiling, necessitates a particularly powerful vacuum device, which must still guarantee adequately high suction power to maintain operating safety even under difficult conditions (intense dust generation and correspondingly rapid fouling of dust filters inside the vacuum device). In the second place, the reduced pressure that can be generated inside the hood—and therefore the suction force that can be achieved against its contact face—is also dependent on adequate planarity of the surface to be ground, which in practice or in the specific application situation is not always the case. In the region of a (more or less) large irregularity of the surface to be ground, the gap between hood and surface to be machined can no longer be “largely” or “completely” sealed, whereby undesired ingress of air under the hood of the grinding head results. Hereby the reduced pressure generated by the vacuum cleaner can collapse immediately, and so the force pulling toward the surface to be ground suddenly disappears or is substantially reduced. The same problem may also occur due to operator errors, for example when the operator working with the grinding machine tilts the grinding head by a clumsy movement, whereby the reduced pressure previously prevailing in the hood suddenly collapses. The grinding machine, which at that moment may not be held adequately securely by the operator, may then separate from the ceiling (or wall) to be ground and—while the grinding plate is turning at high speed—drop to the floor, thus posing a considerable risk of injury for the operator or any other person in the vicinity. And, finally, the slip rings provided in the cited prior art are subject to rapid abrasive wear, which also leads to progressive deterioration of the necessary sealing or throttling effect of such a slip ring. Thus the slip rings must be frequently replaced in order to achieve the best possible reduced pressure.
And, finally, WO 2007/093874 A1 shows a floor grinding machine as well as a grinding disk provided therefor. The grinding disk is equipped on a mounting face turned toward the disk to be ground with a plurality of mutually independent grinding elements, which can be mounted detachably on the mounting face. However, the said floor grinding machine is not suitable for grinding ceilings, and beyond this it is neither described nor known that the said grinding elements are suitable for generating a reduced pressure.